lkml.org 
[lkml]   [2005]   [Mar]   [14]   [last100]   RSS Feed
Views: [more markup]  [less markup]  [headers]  [forward] 
 
Messages in this thread
/
DateMon, 14 Mar 2005 19:03:46 +1100
FromNick Piggin <>
SubjectRe: [PATCH] break_lock forever broken
Ingo Molnar wrote:
> * Hugh Dickins <hugh@veritas.com> wrote:
>
>
>>@@ -187,6 +187,8 @@ void __lockfunc _##op##_lock(locktype##_
>> cpu_relax(); \
>> preempt_disable(); \
>> } \
>>+ if ((lock)->break_lock) \
>>+ (lock)->break_lock = 0; \
>
>
> while writing the ->break_lock feature i intentionally avoided overhead
> in the spinlock fastpath. A better solution for the bug you noticed is
> to clear the break_lock flag in places that use need_lock_break()
> explicitly.
>

What happens if break_lock gets set by random contention on the
lock somewhere (with no need_lock_break or cond_resched_lock)?
Next time it goes through a lockbreak will (may) be a false positive.

I think I'd prefer the additional lock overhead of Hugh's patch if
it gives better behaviour. I think. Any idea what the overhead actually
is?

> One robust way for that seems to be to make the need_lock_break() macro
> clear the flag if it sees it set, and to make all the other (internal)
> users use __need_lock_break() that doesnt clear the flag. I'll cook up a
> patch for this.
>

If you do this exactly as you describe, then you'll break
cond_resched_lock (eg. for the copy_page_range path), won't you?


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 14:11    [from the cache]
©2003-2009